Obviously this is server-side error. I cannot tell why it works with other clients. Filezilla uses internally PSFTP. Maybe you can use PSFTP for testing as it allows more verbose logging._________________Martin Prikryl

Hi, prikryl
actually you were right, this is a server-side issue (a bit tricky!)
I understand also why other clients worked (because they are more "tolerant" and for example Filezilla uses same MessageNumber (probably CuteFtp as well), but WinScp uses different for every sent packet.

Thanks again and good luck

P.S. I've found PSFTP app, but it is German only, so I was not able to turn on the verbose mode....